1. Field of the Invention
The present invention relates generally to micro-machined actuators. The present invention also generally relates to methods for manufacturing and operating micro-machined actuators.
2. Description of the Related Art
FIG. 1 illustrates a micro-machined actuator 10 according to the related art. The actuator 10 illustrated includes a stator wafer 20 at the bottom thereof and a rotor wafer 40 above the stator wafer 20. The rotor wafer 40 includes a section, called a micro-mover 50, that is separated from the rest of the rotor wafer 40. The micro-mover 50 is connected to the rest of the rotor wafer 40 via suspensions 60. The wafers 20,40 are bonded together by a bond material 70 that both holds the wafers 20,40 together and separates them a specified distance.
On the surface of the stator wafer 20 closest to the rotor wafer 40 is a series of stator electrodes 80. On the surface of the micro-mover 50 closest to the stator wafer 20 are formed a series of actuator electrodes 90. Although, for the purposes of clarity, only five stator electrodes 80 and four actuator electrodes 90 are illustrated in FIG. 1, typical micro-machined actuators 10 according to the related art include many more electrodes 80,90 than those illustrated.
The stator wafer 20 typical contains the electronics of the actuator 10 and makes up half of the motor that moves the micro-mover 50, as will be discussed below. The stator wafer 20 is typically made from materials that can be micro-machined (e.g., silicon).
The rotor wafer 40 is typically on the order of 100 microns thick. The rotor wafer 40 must also be micro-machinable, hence it too is often made from silicon. As stated above, the micro-mover 50 generally consists of a portion of the rotor wafer 40 that has been separated from the remainder of the rotor wafer 40 but that remains attached by suspensions 60. Hence, the micro-mover 50 is also typically on the order of 100 microns thick and made from a micro-machinable material.
The suspensions 60 are designed to allow the micro-mover 50 to have in-plane motion while restricting the micro-mover 50 out-of-plane motion. In other words, the suspensions 60 are designed to allow the micro-mover 50 to move horizontally relative to the stator wafer 20 and to restrict the micro-mover 50 from moving vertically. A variety of suspensions 60 are known in the art and are designed with different amounts of in-plane compliance and out-of-plane stiffness. However, none of these suspensions 60 can prevent out-of-plane motion completely.
The bond material 70 typically is a metallic, thin-film material. The type of bond material 70 used depends upon several factors. Commonly, the bond material 70 is chosen so as to provide electrical conductivity between the various wafers 20, 40. The bond material 70 is also chosen on its ability to hermetically seal the chamber in which the micro-mover 50 resides.
The stator electrodes 80 consist of inter-digitated metal lines formed on the surface of the stator wafer 20 closest to the micro-mover 50. The actuator electrodes 90 are another set of inter-digitated metal lines formed on the micro-mover 50. Each metal line that makes up an electrode 80,90 is approximately one to two microns wide and can have a length of up to one or two millimeters. A one to two micron gap typically exists between any two electrodes 80,90.
The actuator electrodes 90 typically cover a substantial portion of the micro-mover 50, which itself can have a total area of between one and two square millimeters. The electrodes 80,90 can be made up of various metals that are generally compatible with semiconductors. Such metals include, but are not limited to, molybdenum, aluminum and titanium.
FIG. 2 illustrates a cross-sectional view of a micro-machined actuator 10 taken across the plane Axe2x80x94A defined in FIG. 1. In operation, the actuator 10 operates by moving the micro-mover 50 relative to the stator wafer 20. In order to move the micro-mover 50 relative to the stator wafer 20, the voltages of selected stator electrodes 80 and actuator electrodes 90 are raised and lowered in a specific pattern in order to alter the electric fields emanating from the electrodes 80,90.
For example, the actuators electrodes 90 can have their voltages set in a pattern where a first electrode 90 would be placed at an operating voltage such as 40 volts, the electrode 90 adjacent to it would be grounded, the next electrode 90 would be at 40 volts, and the remaining electrodes would have their voltages set in a similar manner. The stator 80, on the other hand, could have their voltages set in a pattern that is not quite alternating. For example, a first stator electrode 80 could be set to a high voltage, a second stator electrode 80 immediately adjacent to the first could be set to a low voltage, a third stator electrode 80 adjacent to the second could be set to a high voltage, a fourth stator electrode 80 adjacent to the third could be set to a low voltage, adjacent fifth and sixth stator electrodes 80 could be set to high voltages and a seventh adjacent stator electrode 80 could be set to a low voltage. This seven-electrode 80 voltage pattern could then be repeated for all of the stator electrodes 80 in the actuator 10.
In order to move the micro-mover 50, the pattern of the voltages in the stator electrodes 80 is changed by increasing or decreasing the voltage on one or more of the stator electrodes 80. Such voltages changes alter the distribution of the electric fields present between the stator electrodes 80 and actuator electrodes 90. Therefore, the attractive and repulsive forces between the stator electrodes 80 and actuator electrodes 90 are also altered and the position of the micro-mover 50 is changed until these forces are balanced.
In other words, as the stator electrode 80 voltages are changed, new, low-energy potential regions are created where the forces generated by the electric fields balance the mechanical forces exerted on the micro-mover 50 by the suspensions 60. Hence, once the voltages of the stator electrodes 80 have been changed to a new pattern, the micro-mover 50 repositions itself.
An unwanted side effect of the electric fields is the out-of-plane component of the attractive forces between the stator electrodes 80 and the actuator electrodes 90. These attractive forces pull the micro-mover 50 towards the stator wafer 20 and, if too great, allow the actuator electrodes 90 and stator electrodes 80 to come into close enough contact that they electrically xe2x80x9cshort outxe2x80x9d and fuse together. Such an event causes catastrophic failure of the actuator 10.
Although the suspension 60 is designed to be sufficiently stiff to restrict the out-of-plane movement of the micro-mover 50, it is difficult to design a suspension 60 that simultaneously provides the required in-plane mobility of the micro-mover 50 and restricts out-of-plane motion. Hence, to date, micro-machined actuators 10 have been susceptible to catastrophic failure.
Fusing of the stator electrodes 80 and the actuators electrodes 90 can also occur if an external jolt is applied to the system. For example, if the micro-chip that contains the micro-machined actuator 10 is tapped or jolted, enough additional physical force in the out-of-plane direction could be transferred to the micro-mover 50 and stator wafer 20 configuration to sufficiently overcome the suspension 60 stiffness and to fuse together the stator electrodes 80 and actuator electrodes 90.
Hence, what is needed is a micro-actuator that prevents out-of-plane motion of the micro-mover relative to the stator wafer.
What is also needed is a micro-actuator capable of being tapped or jolted, for example, without having the outside force cause catastrophic failure of the device.
According to one embodiment, an actuator that includes a stator wafer, a first stator electrode protruding from a first surface of the stator wafer, a micro-mover above the first surface of the stator wafer, a first actuator electrode protruding from a first surface of the micro mover, wherein the first surface of the micro-mover and the first surface of the stator face each other, and a first bumper positioned between the stator wafer and the micro-mover.
According to another embodiment, a method of operating a micro-mover that includes providing a stator wafer and a micro-mover over the stator wafer, forming stator electrodes on the stator wafer and actuator electrodes on the micro-mover, moving the micro-mover relative to the actuator electrode by altering the voltages of selected stator electrodes over time, and preventing physical contact between the stator electrodes and actuator electrodes.
According to yet another embodiment, a method of manufacturing an actuator that includes providing a stator with stator electrodes on a first surface of the stator, providing a micro-mover with actuator electrodes on a first surface of the micro-mover, positioning the first surface of the micro-mover facing the first surface of the stator, and providing a bumper between the stator and the micro-mover.